HYPOTHESIS: HCO3ATPase activity is directly related to the level of H-ion secretion in the distal nephron and does not appear to change when proximal tubular H-ion secretion changes. OBJECTIVES: 1) Isolation, partial purification and biochemical characterization of HCO3ATPase in rat renal medulla and papilla. 2) Elucidation of the possible role of this enzyme system in rat brush border membranes, medulla and papilla during states in which H-ion secretion is altered differentially in various parts of the nephron. Investigations I have performed over the past year suggest that HCO3ATPase activity is related to H-ion secretion in the early and late portions of the collecting duct, fragments of which are found in renal medulla and papilla homogenates, respectively. It does not appear to be involved in H-ion secretion in the cortex, nor does activity correlate with systemic acid-base status and thus does not correlate with proximal tubular H-ion secretion. These findings are of major significance in that they represent the first systematic investigation of the physiologic role of this enzyme in different portions of the renal tissue. There is no evidence in the literature regarding the isolation, purification, localization or characteristics of this enzyme in renal medulla and papilla. It is possible that the cortical fraction containing crude brush border membrane was not sensitive enough to detect small changes in HCO3ATPase activity, thus the enzyme will be isolated from purified brush broder membranes. 3) To more precisely define a physiologic role for this enzyme chronic experiments will be designed which will alter H-ion secretion in the distal nephron in different directions while maintaining similar systemic acid-base status. For example, the metabolic alkalosis induced by HCO3 loading is associated with a marked decrease in distal H-ion secretion, while that of mineralocorticoid excess and K-ion depletion is associated with an increase in distal H-ion secretion. If the hypothesis is correct one would expect to see an increase in medullary and/or papillary HCO3ATPase in the latter and not in for former. 4) HCO3ATPase will be measured in turtle bladder (collecting duct model) in chronic metabolic acidosis and alkalosis.